Suna knew. He knew that this relationship wouldn't last, he knew that the person you fell in love with wasn't him and he knew how mutually toxic this was for both of you.

So why did he keep holding on?

"So, what?" he asks with a slight snarl, it wouldn't be Suna if his ego didn't get in the way a little bit, even if he knew he was in the wrong, "Shit gets a little hard, and now you wanna just run away? Give up? Is our relationship really that meaningless to you?!"